GEA24 and Other Wiring

Time: 8hrs

Over the past few days I’ve been doing some wiring while waiting for the parts from TAF and the hoses from Aircraft Specialty. I’m not done with the work I wanted to get done, but I figured I should post the progress since I haven’t posted in a while. I’ll be using the Garmin G3X so the Engine Management System module that is used with that is the GEA24. There is also an older GSU73 EMS that incorporates the ADHARS and a few other components, but the GEA24 seems to be more of the standard now. The wiring of the GEA24 is fairly straight forward, there are a few instances where some extra electronic components are needed. One connection is the Tach (RPM) input from the Rotax trigger coil and also a resistor need for the oil pressure sensors. There is a Garmin kit #011-02348-00 which contains all fo the these miscellaneous diodes and resistors, but it’s a bit hard to find. I did manage to find it on a site called Gardner Lowe Aviation Services so I’m hoping that works out. The kit also comes with the more encompassing Garmin Rotax Sensor kit, but I didn’t buy that since there were components that I wasn’t going to use from that. If all else fails I’ll buy the components separately.

One point of confusion for me was how to wire up the temperature sensors. Rotax provides the oil and cylinder/water temperature sensors (I added the airbox sensor). These are essentially VDO resistive sensors, they have one wired connection and ground themselves to the engine block. I did a little looking and found that the RV12 which uses the Rotax 912 uses a single conductor out to the sensor. I saw at TAF (and confirmed with a few other builders) that they ran a 2 conductor shielded wire out to each sensor. One conductor connects to the sensor and the other to the engine block close to the sensor. I also asked Garmin and they said that the “LO” pin needs to be grounded, however from the RV G3X wiring diagram this isn’t the case and even if the pin needs to be grounded grounding back to the main ground block should be sufficient since the main ground block also connect to the engine block. Now having multiple grounds out to each sensor does provide some redundancy which is nice, but it could also cause some potential ground loops. In the end I decided to follow the RV way and not ground the “LO” pin at all. If the sensors don’t work I can pretty easily run a ground from the 4 “LO” pins (one for each temp sensor) to the main ground block.

I also did quite a bit of organizing and clean up of the other fuselage cable runs. I needed to cut back the cable sleeves and permanently label the wire bundles. Grounds will run back to the main ground block on the inside of the firewall. I installed some wire tie brackets to run cables along the top rib. Additionally I made some brackets that I attached to the support which I used to bot a few adel clamps onto so that the cable can run up and out of the center console area without fear of having it rub on any metal edges.

Edge grommet installed for all the sensor wires to pass through the top rib. The GEA24 will be mounted to the right of the hole. I left a bit of wire as a service loop so it’s easier to work on the connectors.

The GEA24 connectors mostly wired up. I’ll need to finish up the RPM and oil pressure wiring once I get the Garmin kit.

I didn’t realize how blurry this photo was until now. I’ll have to retake it tomorrow. This photo has the GEA24 connectors pretty much done with the inexpensive Chinese knock-off GEA24 installed :-). I cut back the wire sleeves on all the cables and labeled them. The grounds are run through the center hole in the top rib (Need to install edge grommet). Now that the cable is all organized it doesn’t feel so daunting of a task to wire everything up.  I’ll need to purchase a few of the avionics that get mounted on the top rib now (GEA24, TCW battery backup, and the VPX)

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